The present invention relates generally to air bags of the type utilized in vehicle occupant restraint systems.
Motor vehicles in service today are commonly equipped with air bag systems to supplement the protection provided by seatbelts. These air bag systems utilize at least one folded air bag in fluid communication with a source of inflation gas. A sensor is provided to detect a collision between the vehicle and another object. When such a collision is detected, the sensor actuates the source of inflation gas. As a result, the air bag is rapidly expanded to absorb at least a portion of the collision force that would otherwise have been imparted to the vehicle occupant.
Traditionally, a folded air bag is housed in the steering wheel and expanded when a collision is detected so as to protect the driver. A second air bag has been housed in the dash to protect an occupant located in the front passenger seat. In either of these cases, it is important to design the air bag such that it will quickly deflate after it is inflated by the inflation gas. As a result, the air bag will collapse in a controlled manner as it is impacted by the vehicle occupant. Adequate support will thereby be provided to the vehicle occupant without excessive rebounding.
Due to various considerations, driver side air bags and passenger side air bags have often been constructed of different materials. For example, passenger side air bags have often been constructed of uncoated fabric. Driver side air bags, in contrast, have frequently been constructed of a base fabric woven from either nylon or polyester yarns, which has been coated with an appropriate elastomeric material to reduce permeability. Both passenger side and driver side air bags are often equipped with relatively large vent holes through which the inflation gas is expelled.
In addition to driver side and passenger side air bags, many vehicles are now being equipped with air bags known as side cushions (or “side bags”), side curtains, or both. Side cushions are typically mounted in the outboard side of the seat, whereas side curtains are typically mounted along the roof rail of the vehicle. The side cushions are useful in protecting the middle and lower abdomen region of the occupant's body. Side curtains shield against breaking window glass and offer a degree of protection to the occupant's head.
In contrast to driver side and passenger side air bags, both side cushions and side curtains must remain inflated for relatively lengthy periods of time for continuous protection of the vehicle occupants. This is because the side of the vehicle is vulnerable upon impact to penetration of another vehicle or object. Thus, it is not unusual for vehicle manufacturers to require devices designed for side impact protection to remain inflated for several seconds.
The art has provided three primary techniques for the production of side curtains. The first such technique is to produce a one-piece side curtain using a jacquard loom. The one-piece curtain is coated with a suitable silicone or urethane material to increase its air holding capability. A layer of nonwoven material may be provided on the outside of the curtain nearest the door window to inhibit glass penetration. While these cushions have worked well for their intended purpose, the use of jacquard looms is not without disadvantages.
For example, jacquard looms are generally much more expensive than standard flat weaving equipment. In addition, due to the nature of the jacquard weaving process, a fabric defect often results in loss of the entire bag. There is also difficulty in keeping the bag at the correct dimensions because the dimensions are produced in the weaving process itself. Moreover, it is relatively difficult to coat a one-piece bag.
The second technique used to produce side curtains is the traditional “cut and sew” method. According to this technique, pieces of precoated fabric are cut and sewn together to yield a bag of the desired shape. Because seams are stitched through the coated fabric, however, the traditional cut and sew technique produces holes in the coated fabric that can give rise to air leakage. To alleviate this problem, the seams are often treated with a silicone spray or adhesive to plug the sew holes. In addition, the cut and sew technique is relatively labor intensive, and can produce undesirable variations from bag-to-bag when complex sewing patterns are required.
A third technique involves the production of side curtains using flat fabric coated with urethane. One advantage of urethane-coated fabric is that it can be welded to itself using RF or ultrasonic technology, thus eliminating the need to puncture the coated fabric with a needle as it is seamed. The pieces are still cut as in the cut and sew technique, however, and seamed together using a seaming machine that is operated in a manner similar to a traditional sewing machine.